1. Field
Apparatuses and methods disclosed with respect to the exemplary embodiments described herein relate to a DC/DC converter, an electronic apparatus having the same and a DC/DC conversion method thereof. More particularly, disclosed herein are a DC/DC converter, an electronic apparatus having the same and a DC/DC conversion method thereof which synchronizes an output voltage through a switch in a multi-output DC/DC converter.
2. Description of the Related Art
An electronic apparatus including a display apparatus such as a TV has a power supply within or outside thereof to receive necessary power. The power supply may include a DC/DC converter to supply DC power to the electronic apparatus.
Such a DC/DC converter may be provided as a multi-output DC/DC converter to supply a plurality of output power depending on an applied electronic apparatus.
FIG. 1 illustrates a conventional multi-output DC/DC converter.
As shown therein, a conventional multi-output DC/DC converter includes a main switching unit 11 which generates a high frequency square wave, first and second resonance converters 12 and 13, first and second output units 14 and 15, a main switching controller 16, a sync circuit 17 which synchronizes switching frequencies of the main switching unit 11 and a sync switch Q3 of the second output unit 15, and a sync switching controller 18 which controls a switching operation of the sync switch Q3. The sync circuit 17 includes a pulse transformer 17a and a triangular wave generating circuit 17b. The sync switching controller 18 includes first and second comparison elements 18a and 18b and a gate driving circuit 18c. 
Commercial AC power is corrected and adjusted in power factor by a power factor correction (PFC) and output as a DC voltage Vin to the main switching unit 11. The main switching unit 11 is switched on and off alternately by switches Q1 and Q2 according to a switching frequency to flow or block current and changes the input DC voltage Vin into a square wave and transmits the square wave to the first and second resonance converters 12 and 13. The first and second resonance converters 12 and 13 include LC resonance circuits, and convert AC square wave voltage, which has been transmitted by the main switching unit 11, into AC sine wave current and transmit the current to the first and second output units 14 and 15. First output power Vs of the first output unit 14 is transmitted to the main switching controller 16 to control the main switching unit 11. Second output power Va of the second output unit 15 is transmitted to the sync circuit 17, and an output signal of the sync circuit 17 is applied to a sync switch Q3 of the second output unit 15 to control the second output power Va.
The main switching controller 16 receives the first output power Vs and outputs a driving signal to control a switching operation of the Q1 and Q2 of the main switching unit 11. The driving signal of the main switching unit 11 is transmitted to a secondary side of a transformer through the pulse transformer 17a, and transmitted to the second comparison element 18b through the triangular wave generating circuit 17b including an RC filter and an auxiliary switch Qsaw. The triangular wave generating circuit 17b generates and outputs to the second comparison element 18b a triangular wave signal Vsaw which is synchronized with the driving signal of the main switching unit 11.
The second output power Va is applied to the first comparison element 18a, and the second comparison element 18b compares the output signal of the first comparison element 18a with the signal generated by the triangular wave generating circuit 17b and generates a control pulse, which is transmitted to the Q3 through the gate driving circuit 18c. 
The pulse transformer 17a in FIG. 1 transmits the driving signal of the main switching unit 11 input to the primary side of the transformer, and thus should overcome a high insulating voltage of the primary and secondary sides and requires multiple windings to generate auxiliary power for driving an integrated circuit (IC). Accordingly, to satisfy the foregoing requirements, there arises a problem of providing a large and expensive pulse transformer 17a. 
FIG. 2 illustrates a waveform of an input/output signal of the second comparison element 18b in FIG. 1.
The second comparison element 18b compares the triangular wave signal Vsaw generated by the triangular wave generating circuit 17b with the output signal Vref2 of the first comparison element 18a and generates a driving voltage of Q3. More specifically, as shown in FIG. 2, the output signal SW3 of the sync switching controller 18 outputs 0 if Vref2 is larger than Vsaw, and outputs 1 if Vref2 is smaller than Vsaw. Q3 is synchronized with the main switching unit 11 by the output signal SW3.
However, during the operation of the circuit, the maximum value of the triangular wave Vsaw of the conventional multi-output DC/DC converter may not be maintained consistently. For example, if the switching frequency is large, the maximum value of the triangular wave may be decreased. If the switching frequency is small, the maximum value of the triangular wave may be increased. Accordingly, to precisely control Va through Q3, Vref2 should be fluctuated according to the fluctuation of Vsaw. However, it is difficult to control the output value Vref2 by the first comparison element 18a in real-time.
The conventional multi-output DC/DC converter in FIG. 1 needs an additional gate driving circuit 18c, e.g. a totem-pole circuit to drive a high side gate to thereby operate Q3. Also, upon an increase in the number of auxiliary power Va (i.e., the number of output units) driven by the sync switch Q3 other than the main output power Vs, the number of the sync switching controller 18 is increased accordingly. As the number of parts and costs for the circuit is increased, it is not easy to extend the number of output voltages.